Facile Reductive Silylation of UO₂²⁺ to Uranium(IV) Chloride

Abstract

General reductive silylation of the UO cation occurs readily in a one-pot, two-step stoichiometric reaction at room temperature to form uranium(IV) siloxides. Addition of two equivalents of an alkylating reagent to UO X (L) (X=Cl, Br, I, OTf; L=triphenylphosphine oxide, 2,2'-bipyridyl) followed by two equivalents of a silyl (pseudo)halide, R Si-X (R=aryl, alkyl, H; X=Cl, Br, I, OTf, SPh), cleanly affords (R SiO) UX (L) in high yields. Support is included for the key step in the process, reduction of U to U . This procedure is applicable to a wide range of commercially available uranyl salts, silyl halides, and alkylating reagents. Under this protocol, one equivalent of SiCl or two equivalents of Me SiCl results in direct conversion of the uranyl to uranium(IV) tetrachloride. Full spectroscopic and structural characterization of the siloxide products is reported.

The effect of iron binding on uranyl(v) stability

“… 18 A second irreversible redox event is observed at E 1/2 = –2.47 V vs. Fc/Fc + for complex 2 , but not for complex 1 . This event is consistent with the reduction of the metal centre (values of redox potential ranging from –2.02 to –2.88 V vs. Fc/Fc + were previously assigned to the U( v )/U( iv ) couple 12 a ). The possibility that this event could be related to the reduction of the Schiff base ligand is unlikely since this feature is absent from the voltammograms of the H 3 trensal, K 3 trensal ligands and of the complex 1 .…”

“…Moreover, it has been demonstrated that the binding of strong Lewis acids such as B(C 6 F 5 ) 3 to the uranyl( v ) oxo groups renders more accessible the reduction of U( v ) to U( iv ). 10d , 11 , 12 A fewer studies have been directed to investigate the effect of the interaction of uranyl( v ) with 3d transition metals on the stability and redox reactivity of uranyl( v ) species. Moreover, in spite of the fact that several uranyl( v ) complexes stable in organic solution have been isolated in recent years, 9 , 13 only a few examples of heteropolymetallic complexes presenting a UO 2 + ···M interaction, where M is a 3d transition metal, have been prepared.…”

Ligand‐Supported Facile Conversion of Uranyl(VI) into Uranium(IV) in Organic and Aqueous Media

“…The 1 H NMR spectrum of the reaction mixture, when compared to the spectrum of 2 in D 2 O at pH 8.5, revealed the quantitative conversion of 1 into the uranyl(V) species [UO 2 (dpaea)] À (Scheme 2; Supporting Information, Figure S4). Crystals of (6) were obtained by slow evaporation of the H 2 O solution at room temperature ( Figure 2; Supporting Information, Figure S21). The structure shows a dimer with two anionic {UO 2 (dpaea)(H 2 O)} À moieties bridged by two Na cations binding the carboxylate oxygen atoms.…”

Ligand‐Supported Facile Conversion of Uranyl(VI) into Uranium(IV) in Organic and Aqueous Media

“…Significant progress has been made in recent years in the development of systems that allowed the reduction of uranyl(VI) to uranyl(V) . In contrast, fewer examples of controlled reduction of uranyl(VI) and uranyl(V) complexes to well‐defined U IV compounds have been reported and they all require the preliminary functionalization of the two uranyl oxo ligands with Lewis acids or metal cations…”